If one machine still boots to PXE and run something like a hardware inventory, then I wouldn’t think it is the TFTP password. Schedule a hardware inventory task for a machine in the 192.168.10.x network and make sure that works.
If that works. Try to schedule a task for a machine in the 192.168.12.x network. Schedule it through the web interface, then check the /tftpboot/pxelinux.cfg/ folder for a task file matching your machine (01-mac-address-of-machine). If you get a file in that folder, paste the contents into this thread (use code tags).